The objective of this research is to clarify the mechanisms responsible for the suppression of soot in flames by fuel additives. Measurements are limited to well-defined hydrocarbon air prevaporized liquid- and gaseous-fueled flames. Gas-phase hydrocarbon species measurements have been made in an axisymmetric prevaporized iso-octane/air diffusion flame with and without ferrocene present as a fuel additive. The concentrations have been determined using quartz probe sampling and chromatographic analysis. Of the roughly twenty species detected, most were unaffected by the ferrocene. Expections were C2H2 and H2 which showed a decrease and increase, respectively, with ferrocene seeding. Solid effluent has been collected and analyzed by ESCA (Electron Scattering for Chemical Analysis) for the seeded flame. For seeding levels sufficient to suppress a soot plume, the effluent was hematite. Keywords: Ferrocene; Flame; Soot; Fire prevention.